1. Field of the Invention
The invention relates to a roller pump for medical technology, in particular for conveying blood in extracorporeal circulations. This roller pump has a stator with a cylindrical hollow space, the wall structure of which, commonly designated as the pump bed in the field of this technology, is formed as a support wall for a pump tube led along this wall about the central longitudinal axis of the hollow space. A pump rotor in the pump stator is rotateable about its central longitudinal axis, the rotor having rollers rotatably supported on roller supports, the rollers rolling along the tube and compressing this upon rotation of the rotor. The support wall of the pump rotor has an opening with an inlet and an outlet region for the tube and in which regions this support wall received from the circular path of motion of the pump rollers with a curvature in the same direction as this path of motion.
2. Discussion of the Prior Art
A roller pump of this kind is known from DE-B-33 26 786. As a rule, such a roller pump has two rollers which are diametrically opposed with reference to the rotational axis of the rotor. The pump rollers push the pump tube together to such an extent along a larger portion of the circumference of the support wall that the interior of the pump tube is occluded in a liquid-tight manner at this location. On account of the rolling along of the pump rollers when the stator turns, the occlusions of the tube travel with the rollers, the liquid in the tube in front of the occlusions being further transported in the rotational direction of the stator. The tube recedes from the roller path in the region of the inlet and outlet opening, on account of which the rollers increasingly lift away from the tube in the outlet region of the pump stator arranged in front of this opening in the rotor direction, while they increasingly press into the tube in the inlet region which follows in the rotational direction. On account of the provision of at least two pump rollers, at least one roller presses against the pump tube for each position of the roller so that a further transport of the pumping medium is guaranteed.
During pivoting of the pumping rollers towards and away from the tube, the momentary pumping stream of the pump varies. Thus, the momentary pumping stream of the pump reduces to the extent of the tube volume which is generated in the tube during the pivoting away of the rollers on account of the ensuing removal of the tube occlusion. In unfavorable cases, a deflection of the flow direction can occur at the outlet cross-section of the tube, this being accompanied by large forces which result on account of the mass moment of inertia of the pumping medium and lead to the danger of considerable blood damage. The minimalization of this pressure pulsation conditional upon this principle is a considerable prerequisite for the use of roller pumps for pumping blood, as it can lead to a large damage rate (haemolysis) of cells on account of the high proportion of sensitive cell components in the blood.
In the previously known roller pumps, the roller supports are pressed strongly in a radial direction outwardly against the tube, whereas the inventive support wall of the pump bed has a curvature in the same direction as the circular path of the rollers in the outlet region, the curvature having a continuously increasing radius of curvature in the rotational direction of the rollers. This is to ensure substantial independence from the cross-section of the pump tube used as well as an occlusion of the pump tube with a defined spring force in the case of varying operational conditions while pressure pulsations in the pumping medium are substantially reduced. On account of this shape of the curvature path in the outlet region of the support wall, the pivoting of the roller away from the pump tube is extended over a larger rotational angle. On account of this, the pumping medium within the pumping tube on the pressure side has the possibility to slowly and continuously compensate the volume increase occurring on account of the pivoting of the pump rollers away from the tube and the removal of the occlusion, on account of which a reduced pulsation behavior ensues.
However, it has been discovered that it is essential for preventing damage of the cell components in blood that the occurring unavoidable reduction in the pump throughflow during pivoting of the pump rollers away from the tube has gradients which are as flat as possible in order to minimise the mass moment of an inertia and the pressure pulsation resulting from this, in particular the negative delayed pressure peaks.